Abstract

Migration timing has evolved in many animals, allowing them to maximize breeding and feeding success by matching seasonal changes in abiotic conditions and resource pulses. These seasonal changes can shift with the climate, resulting in mismatches between migrations and resource availability unless the populations respond through phenotypic plasticity or evolutionary adaptation. It is common, however, for factors unrelated to climate to affect phenology. Salmon are an exceptionally well-studied group of fishes whose breeding migrations can serve as a template to consider the complex factors affecting migration phenology. In this paper, hypotheses for explaining changes in adult salmon migration phenology are reviewed. Pathways through which climate change may influence migration timing are first summarized, including shifting migration cues, limiting freshwater conditions, changes in distribution and conditions at sea, and alterations in embryo development. Alternative causes of phenological change in salmon are then explored including anthropogenic modifications of river habitat, demographic effects, hatcheries, and fisheries. The effects of these factors on phenology can mimic and mask climate effects, making it challenging to disentangle the causal basis of observed patterns. Instead of inferring shifts from trends in timing data (as is often done), it is suggested that specific mechanistic hypotheses be proposed and tested rigorously, and alternative causes systematically ruled out. Overall, it is challenging to attribute causation to phenological change, but salmon exemplify the many ways in which migration timing can change, including shifts due to climate and other processes.

摘要

许多动物的迁徙时间已经发生变化，通过匹配非生物条件和资源脉冲的季节性变化，使它们能够最大限度地繁殖和喂养成功。这些季节性变化会随着气候变化，导致迁徙和资源可用性之间的不匹配，除非种群通过表型可塑性或进化适应做出反应。然而，与气候无关的因素影响物候是很常见的。鲑鱼是一种研究得非常好的鱼类，其繁殖迁徙可以作为考虑影响迁徙物候的复杂因素的模板。在本文中，回顾了解释成年鲑鱼迁徙物候变化的假设。首先总结了气候变化可能影响移民时间的途径，包括不断变化的移民线索，限制淡水条件、海洋分布和条件的变化以及胚胎发育的改变。然后探索鲑鱼物候变化的其他原因，包括河流栖息地的人为改变、人口影响、孵化场和渔业。这些因素对物候学的影响可以模仿和掩盖气候影响，使得解开观察到的模式的因果基础具有挑战性。与其从时间数据的趋势中推断出变化（正如经常所做的那样），建议提出具体的机械假设并进行严格的测试，并系统地排除其他原因。总体而言，将因果关系归因于物候变化具有挑战性，但鲑鱼体现了迁移时间可能发生变化的多种方式，包括气候和其他过程引起的变化。